Rising floodwaters from the remnants of Hurricane Harvey sent thousands of people scrambling on to rooftops or higher ground in Houston, overwhelming rescuers who fielded countless desperate calls for help.
Leaving two people dead in its wake, Harvey was downgraded to a tropical storm on Saturday but was no less deadly.
A fleet of helicopters, airboats and high-water vehicles confronted flooding so widespread that authorities had trouble pinpointing the worst areas.
The water rose high enough to begin filling second floors. People used inflatable beach toys, rubber rafts and even air mattresses to get through the rising waters to safety. Others simply waded while carrying plastic trash bags stuffed with their belongings.
Harris County Sheriff Ed Gonzalez used Twitter to field calls for assistance. Among those seeking help was a woman who posted: "I have 2 children with me and the water is swallowing us up."
I have 2 children with me and tge,water is swallowing us up. Please send help.
911 is not responding!!!!!!— Maritza RITZ Willis (@RitzWillis) August 27, 2017
Houston Mayor Sylvester Turner said authorities had received more than 2,000 calls for help and would be opening the city's main convention centre as a shelter.
"I don't need to tell anyone this is a very, very serious and unprecedented storm," Mr Turner told a news conference. "We have several hundred structural flooding reports. We expect that number to rise pretty dramatically."
Rainfall of more than 4 inches per hour resulted in water levels higher than in any recent floods and higher than during Tropical Storm Allison in June 2001, said Jeff Linder of flood control district in Harris County, which includes Houston.
Rescue came by land, water and air.
The Coast Guard, which received more than 300 requests for help, deployed five helicopters and asked for additional aircraft from New Orleans.
Staff at a Houston television station broadcasting live coverage of the floods had to evacuate after water from the nearby Buffalo Bayou started to gush into the building.
The director of the Federal Emergency Management Agency, Brock Long, said the government expected to conduct a "mass care mission" and predicted that the aftermath of the storm would require FEMA's involvement for years.
"This disaster's going to be a landmark event."
President Donald Trump tweeted Sunday morning that he would visit Texas.
"I will be going to Texas as soon as that trip can be made without causing disruption," the president posted on Twitter. "The focus must be life and safety."
I will be going to Texas as soon as that trip can be made without causing disruption. The focus must be life and safety.— Donald J. Trump (@realDonaldTrump) August 27, 2017
The rescues unfolded a day after the hurricane settled over the Texas coastline. It was blamed for killing at least two people and injuring up to 14.
Anxiety ran high throughout the region between Corpus Christi and Houston because some of the areas with the greatest hurricane damage were inaccessible to rescuers.
And the forecast for days of steady rain threatened to inundate the region's flat landscape with as much as 40 inches (100 centimetres).
Some of the worst damage appeared to be in Rockport, a coastal city of about 10,000 that was directly in the storm's path. The mayor said his community took a blow "right on the nose" that left "widespread devastation," including homes, businesses and schools that were heavily damaged. Some structures were destroyed.
One person was killed in Aransas County, county Judge C.H. "Burt" Mills Jr. said.
Another person - a woman who tried to get out of her vehicle in high water - died in flooding in Harris County, where Houston is located.
Meanwhile, the storm was barely moving. Rainfall totals varied across the region, with Galveston receiving around 8 inches (20 centimetres), Houston 11 (28 centimetres) and Aransas 10 (25 centimetres). Tiny Austwell got 15 inches (38 centimetres).
The fiercest hurricane to hit the US in more than a decade came ashore late Friday as a mammoth Category 4 storm with 130 mph (209 kph) winds.
Harvey weakened on Saturday to a tropical storm. By Sunday morning the system was centred about 65 miles south-east of San Antonio, with maximum sustained winds of about 45 mph (72.42 kph), according to the National Hurricane Centre, which described the flooding as "catastrophic."